1. Field of the Invention
The present invention relates to a built-in antenna for a portable terminal. More particularly, the present invention relates to a built-in antenna for a portable terminal, which enhances a radiation characteristic of a Printed circuit board Embedded Antenna (PEA) and reduces a Specific Absorption Rate (SAR) of electromagnetic waves.
2. Description of the Related Art
Since portable wireless terminals (hereinafter, referred to as potable terminals) were initially developed, increased services and functions have been developed. Services, which had supported conventional voice communications, are currently extended from transmitting short messages and pictures to Internet and broadcasting services. In addition to a simple communication function, functions such as a camera function and an MPEG Audio Layer 3 (MP3) function have been provided to terminals, and display of the terminals have changed from black-and-white display to high-definition color Liquid Crystal Display (LCD) display. While the number of communicable services in one band was two or three, six or more services are currently used in one band. The sizes of current terminals have been developed to be lighter and slimmer than those of initial terminals. This is because elements built in the terminals are designed to be very small in size and very high in performance. However, there is no exception to terminal antennas. While initial terminal antennas secured only single or two service bands as external type antennas, current terminal antennas secure at least four to six service bands or more as built-in type antennas. Further, the size of the current terminal antennas has considerably decreased. In view of antenna performance closely related to the physical size of antennas the antenna conditions have increasingly deteriorated.
Several methods for designing an antenna have been proposed to decrease the physical space of an antenna in a portable terminal in order to secure various high-performance service bands and to reduce manufacturing cost. One representative antenna is a Printed circuit board Embedded Antenna (PEA) that forms a radiation pattern on a substrate surface. The PEA is very important in reducing manufacturing costs of terminals because it's manufacturing costs are low as compared with a carrier-type antenna according to the related art. In addition, the PEA can be implemented smaller than an antenna using a dielectric or magneto dielectric material (hereinafter, referred to as a chip antenna). This is because the PEA does not require 3D cubic space like the carrier-type antenna and the chip antenna according to the related art, but requires only a 2D planar space.
Meanwhile, to develop a high-performance, small antenna in the limited antenna space of a terminal requires considerable costs. In a case where it is impossible to mount the carrier-type antenna, a specific material (i.e., dielectric or magneto dielectric material) should be used. However, the cost of the specific material is expensive. When considering the number of terminal models annually developed by terminal manufacturers and released in the market, the time, cost and manpower necessary for designing antennas and ensuring performance of the antennas are beyond expectation. Whenever a terminal is developed, it is urgently required to reduce the time, cost and manpower necessary for designing an antenna in order to reduce the entire cost and time necessary for manufacturing terminals. Accordingly, profits can be improved in terminal manufacturers, and customers can obtain great economic benefit and convenience.
A carrier type antenna frequently used in designing a multi-band antenna according to the related art requires a certain space, and the shape of the carrier-type antenna also depends on the shape of a terminal case. Therefore, a carrier should be individually designed whenever a terminal is designed. Furthermore, antennas should be manually assembled one by one which results in increased time and cost required to develop antennas. If it is difficult to ensure the performance of the carrier due to the very small antenna space of the terminal, a chip antenna using a dielectric or magneto dielectric material is used. In this case, the cost of the material for the chip antenna is further increased, and increased time is still required to assemble the antenna. As terminals become smaller and slimmer, it becomes increasingly difficult to mount not only the carrier-type antenna but also the chip antenna in a given antenna space. Accordingly, as the PEA has been developed, many problems have been solved in view of the antenna size or material cost, but other problems still exist.
In the case of the carrier-type antenna built in a terminal according to the related art, it is very difficult to apply the carrier-type antenna to a slim terminal. This is because the height of an antenna should be secured to a certain extent and mounting the carrier-type antenna in the slim terminal is impossible due to the height of the carrier-type antenna itself. In a case where the chip antenna is used, the height of the chip-type antenna is smaller than that of the carrier-type antenna, but the height of the chip antenna is also secured to a certain extent. Further, the cost of the chip antenna is about two times greater than that of the carrier-type antenna, and hence it is difficult to apply the chip antenna to the slim terminal.
Therefore, the cost of materials for the antenna should be reduced to decrease the cost of the entire terminal. When a terminal is assembled, the carrier-type antenna or the chip antenna is individually assembled which is inefficient and thus results in increased labor cost.
The PEA has solved many problems of the carrier-type antenna or the chip antenna. However, when the PEA is mounted in a terminal, the position of the PEA is close to a user's head. Therefore, the PEA may have a bad influence on a human body. Further, it is difficult to manufacture a PEA having a service bandwidth that is usable for a multi-band service.